The present invention is directed to an apparatus for and a method of cutting a plurality of grooves in faced duct insulation boards (glass fiber or foam duct insulation boards) and forming the grooved, faced duct insulation boards into tubular liners which can be used to internally line large diameter round and flat oval metal ducts and the grooved duct insulation boards and the large diameter ducts formed thereby.
Heating, ventilating and air conditioning systems found in large building structures, such as, convention centers, sports domes, etc., require large diameter, high capacity, insulated round or flat oval air ducts for conveying conditioned air from air conditioning units to locations throughout the building structure and for returning air to the air conditioning units for heating or cooling and recirculation. These large diameter, insulated round or flat oval air ducts typically range from about twenty inches to over one hundred inches in diameter.
Presently, the most commonly used internally treated, air ducts for such large, high capacity heating, ventilating and air conditioning systems are double wall insulated metal-ducts, such as, the air duct 100 shown in FIG. 11. These large diameter, high capacity, metal air ducts 100 comprise an outer tubular metal shell 102, an inner tubular metal liner 104 (which is typically perforated), and one or more layers of glass fiber or other insulation 106 intermediate the outer tubular shell and the inner tubular liner. These tubular air ducts normally have either a round or a flat oval transverse cross section. Due to their construction, which in essence, comprises a first tubular metal duct contained within a second tubular metal duct, and the labor required to both assemble the first metal duct within the second metal duct and insulate the space between the ducts, these double wall, insulated metal air ducts are costly.
A second insulated air duct 110, currently in use, is shown in FIG. 12. This insulated air duct 110 comprises a round, tubular metal shell 112 internally lined with a round tubular, preformed, self-supporting, molded, glass fiber insulation 114 sold by Schuller International Inc., under the trademark "SPIRACOUSTIC". This air duct system exhibits good thermal and acoustical insulating properties and eliminates the need for the costly perforated metal liner 104 of the air duct 100. However, this system has only been used with tubular metal shells having internal diameters of twenty-four inches or less.
Recently, large diameter, high capacity, air ducts, comprising tubular metal shells lined with coated, glass fiber duct boards, were installed in a high capacity heating, ventilating and air conditioning system. By eliminating the inner tubular metal liner 104 of the double wall, insulated metal air ducts 100 and the labor involved in assembling the tubular metal liner 104 within the outer tubular metal shell 102, the cost of the large diameter, high capacity air duct used in the heating, ventilating and air conditioning system was reduced.
The elimination of the inner tubular metal liner was accomplished by forming a plurality of parallel grooves or kerfs in the airstream surfaces of the duct boards that enabled the duct boards to be curved (about an axis parallel to the grooves or kerfs) to conform to the interior surfaces of the tubular metal shells. The glass fiber duct boards were four feet wide by ten feet long. Where the tubular metal shell being lined had an internal circumference equal to or less than the length of the duct board, the duct board or a portion of the duct board was formed into a tube and inserted into the tubular metal shell to form the insulated air duct. Where the tubular metal shell had an internal circumference greater than the length of one duct board, a first duct board was taped to a second duct board or portion of a duct board to obtain the required length, the joined duct boards were then formed into a tube, and the tube was inserted into the tubular metal shell to form the insulated air duct.
The parallel grooves or kerfs cut into the airstream surfaces of the duct boards were narrow and had sidewalls extending substantially perpendicular to the airstream surfaces. The airstream surfaces of the duct boards were coated to encapsulate the fibers and/or particles of the duct boards within the duct boards. By forming narrow grooves with substantially perpendicular sidewalls in the airstream surfaces, the mouths of the grooves or kerfs closed when the duct boards were curved to conform to the interior surfaces of the tubular metal shells thereby keeping the fibers in the groove or kerf surfaces from being exposed to the interior of the air ducts and the high velocity air stream being conveyed through the air ducts. Vee grooves did not close when the duct boards were curved to conform to the interior surface of the tubular metal shells, exposing fibers in the groove surfaces. Accordingly, vee grooves were not used in the duct boards.
A duct board grooving apparatus using a plurality (thirty or more) of evenly spaced rotatably driven, saw blades was used to cut the grooves or kerfs in the airstream surfaces of the duct boards. The saw blades were mounted on a drive shaft and manually spaced along the drive shaft. The drive shaft had a round transverse cross section. Accordingly, after the saw blades were manually spaced along the drive shaft, the saw blades had to be affixed to the drive shaft by set screws so that the saw blades would rotate with the drive shaft and maintain their axial spacing.
To groove duct boards for lining tubular metal shells of different diameters, the spacing between the numerous saw blades was adjusted, through trial and error, until a spacing was found that allowed the duct boards to be curved to the particular curvature required for the tubular metal shell being lined. Thus, the numerous saw blades each had to be loosened, moved and reaffixed to the drive shaft, a very time consuming operation.
The saw blades used for cutting grooves or kerfs in the duct boards had peripheral teeth projecting radially outward from the saw blades in the planes of the saw blades whereby the sidewalls of the saw blades radially inward of the teeth engaged the sidewalls of the grooves or kerfs creating drag.
The saw blade drive shaft was offset from the axis of a backup roll used to support the duct boards beneath the saw blades as the grooves or kerfs were cut into the airstream surfaces of the duct boards. Accordingly, the duct boards could be deflected somewhat during the grooving operation causing a variation in the depths of the grooves formed across the lengths of the duct boards. In addition, the saw blade drive shaft was supported laterally from an existing tool bar which aggravated the deflection problem.